The effect of inlet and outlet boundary conditions in image-based CFD modeling of aortic flow.
The effect of inlet and outlet boundary conditions in image-based CFD modeling of aortic flow.
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DOI：
10.1186/s12938-018-0497-1
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发表时间：
2018-05-30
影响因子：
3.9
通讯作者：
Kemmerling EMC
中科院分区：
文献类型：
--
作者：
Madhavan S;Kemmerling EMC
心血管流动的计算建模是一个不断发展和有用的领域，但这种模拟通常需要研究人员猜测流动的入口和出口条件，因为它们难以测量且昂贵。关键是要确定这些假设引入的不确定性，以评估心血管血流模拟的准确程度。我们的工作开始解决这个问题，通过检查流量的敏感性，几个不同的假设速度的入口和出口条件下，在患者特定的主动脉模型。我们研究了活塞流、抛物线流、线性剪切流、斜立方流剖面和入口处的沃默斯利流之间的差异。只有入口速度分布的形状是不同的，所有其他参数是相同的，在这些模拟。二次流形式的反向旋转的涡对也被添加到抛物轴向流，以研究其对解决方案的影响。此外，我们还研究了二元Windkessel，三元Windkessel和流出边界条件之间的差异。在这些模拟中，仅改变出口边界条件。结果表明，在不同的进口速度分布形状下，进口附近的轴向速度和面内速度有很大的不同。然而，超过1.75D的解在性质上是相似的，其中D是入口直径。这种趋势也在其他量中观察到，例如压力和壁面剪应力。归一化均方根偏差是不同情况下轴向速度大小差异的量度，通常沿流向坐标沿着减小。线性剪切入口速度边界条件和塞式速度边界条件解具有最高的时均壁面剪应力，近似高于抛物线入口速度边界条件。在进口1D上游，加入二次流对壁面剪应力的时间分布有显著影响。这是特别可观察到的，当综合壁面剪应力大小变化之间的模拟与二次流和没有。出口边界条件研究的结果表明，Windkessel模型与流出边界条件的时均壁面剪应力相差多达。此外，轴向速度幅值的归一化均方根偏差（Windkessel和流出边界条件之间偏差的测量）沿流向坐标沿着增加，表明出口附近的变化较大。有人发现，入口速度条件的选择显着影响只有靠近主动脉入口的流动区域。超过入口远端的两个直径，流量解决方案的差异很小。虽然必须进行额外的研究来验证这一结果，但数据表明，如果研究人员关注非常接近入口的流动细节，则主要使用患者特定的入口条件是很重要的。类似地，出口条件的选择显著地影响出口附近的流动。上游的五个直径近端的出口，出口边界条件之间的偏差检查是微不足道的。虽然入口和出口条件只影响流量显着在其各自的社区，我们的研究表明，出口条件的影响更大的百分比的解决方案域。
Computational modeling of cardiovascular flow is a growing and useful field, but such simulations usually require the researcher to guess the flow’s inlet and outlet conditions since they are difficult and expensive to measure. It is critical to determine the amount of uncertainty introduced by these assumptions in order to evaluate the degree to which cardiovascular flow simulations are accurate. Our work begins to address this question by examining the sensitivity of flow to several different assumed velocity inlet and outlet conditions in a patient-specific aorta model. We examined the differences between plug flow, parabolic flow, linear shear flows, skewed cubic flow profiles, and Womersley flow at the inlet. Only the shape of the inlet velocity profile was varied—all other parameters were identical among these simulations. Secondary flow in the form of a counter-rotating pair of vortices was also added to parabolic axial flow to study its effect on the solution. In addition, we examined the differences between two-element Windkessel, three element Windkessel and the outflow boundary conditions. In these simulations, only the outlet boundary condition was varied. The results show axial and in-plane velocities are considerably different close to the inlet for the cases with different inlet velocity profile shapes. However, the solutions are qualitatively similar beyond 1.75D, where D is the inlet diameter. This trend is also observed in other quantities such as pressure and wall shear stress. Normalized root-mean-square deviation, a measure of axial velocity magnitude differences between the different cases, generally decreases along the streamwise coordinate. The linear shear inlet velocity boundary condition and plug velocity boundary condition solution exhibit the highest time-averaged wall shear stress, approximately higher than the parabolic inlet velocity boundary condition. Upstream of 1D from the inlet, adding secondary flow has a significant impact on temporal wall shear stress distributions. This is especially observable during diastole, when integrated wall shear stress magnitude varies about between simulations with and without secondary flow. The results from the outlet boundary condition study show the Windkessel models differ from the outflow boundary condition by as much as in terms of time-averaged wall shear stress. Furthermore, normalized root-mean-square deviation of axial velocity magnitude, a measure of deviation between Windkessel and the outflow boundary condition, increases along the streamwise coordinate indicating larger variations near outlets. It was found that the selection of inlet velocity conditions significantly affects only the flow region close to the inlet of the aorta. Beyond two diameters distal to the inlet, differences in flow solution are small. Although additional studies must be performed to verify this result, the data suggest that it is important to use patient-specific inlet conditions primarily if the researcher is concerned with the details of the flow very close to the inlet. Similarly, the selection of outlet conditions significantly affects the flow in the vicinity of the outlets. Upstream of five diameters proximal to the outlet, deviations between the outlet boundary conditions examined are insignificant. Although the inlet and outlet conditions only affect the flow significantly in their respective neighborhoods, our study indicates that outlet conditions influence a larger percentage of the solution domain.
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作者：
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DOI：
10.1098/rsif.2016.0073
发表时间：
2016-06
期刊：
Journal of the Royal Society, Interface
影响因子：
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通讯作者：
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